This invention relates generally to flat panel display devices and particularly to a modulator electrode structure for such devices.
Prior art flat panel display devices, such as those described in U.S. Pat. Nos. 4,316,118 and 4,199,705, include a baseplate and a faceplate which are held in a spaced parallel relationship by a plurality of external side walls. A phosphor screen is arranged on the faceplate to produce the desired image when struck by electrons. The envelope is divided into a plurality of channels by internal walls which provide support against collapse due to atmospheric pressure. Each of the channels includes a guide mesh structure along which electron beams propagate the lengths of the channels until one line of the visual display is to be produced. The electrons are emitted from a cathode which is arranged at the entrance to each guide mesh structure. Pairs of modulation electrodes overlap the cathodes so that each electron beam can be individually modulated to produce the desired image on the screen. Interaction of the modulation voltages on adjacent pairs of modulation electrodes is avoided by the use of isolation electrodes between the modulation electrodes. The isolation electrodes are all biased at the same constant voltage. The constant electric field produced by the isolation electrodes prevent the varying electric fields of the modulation voltages from interacting and adversely affecting the modulation of the electron beams.
Flat panel display devices built in accordance with the prior art operate satisfactorily for the purposes intended. However, the emission current density along the cathode between each modulator electrode pair is peaked in the center of the electrode and falls off sharply on each side. A less sharply peaked current distribution would result in the same total beam current being obtained with a smaller value of peak current and would constitute a very desirable improvement.
The instant invention provides this improvement by the provision of a modulator electrode configuration which substantially flattens the current distribution while maintaining the desired value of total beam current.